Composite liner permeation rate

Data about the imperviousness of a faultless liner system under defined boundary conditions for as large a number of pollutants and soil materials as possible form an important component of the characterisation of the efficacy of this liner for instance in comparison to equivalent alternative liner systems. Therefore, in the following, a parameterization will be discussed for the permeation rate (or the permeability) and the induction time for diffusive mass transport in the composite liner consisting of a geomembrane and a compacted clay liner (or more generally a porous mineral material). Quantities, which refer to the geomembranes, will be denoted with index 1, such as thickness d and diffusion coefficient D, and quantities referring to the mineral liner will have index 2 such as thickness d2 and effective diffusion coefficient D2. The porosity of the water-saturated mineral liner is denoted with 0 as above. 

The permeation rate for the difihision of a pollutant through the composite liner is thus determined according to Eqs. 7.35 and 7.36 at specified thicknesses (for example. di = 2.5 mm and J2 = 0.75 m and/or 1.50 m for municipal waste landfill and/or the hazardous waste landfill) by diffusion coefficients Di and Do, partition coefficient cTo,i and as well as by the parameters of the porous mineral material 0 and 77 While the parameters Di and Do as well as 0 and /"vary only by one or two orders of magnitude for different pollutants and mineral materials, the partition coefficients partition coefficient between plastic geomembrane and leachate which characterises the permeation rate of the composite liner for different pollutant classes. The partition coefficient for cations and anions is in practice zero, since they cannot be dissolved in the non-polar medium polyethylene. For the diffusive mass transport therefore only undissociated organic and inorganic molecules have to be taken into consideration. 

Fig. 7.3b. Calculation of the acetone mass diffusing through the composite liner (thickness of the mineral liner (ML) 30 cm) per m as a function of time. The slope of the straight line yields the permeation rate and its time axis intercept provides the induction time. The induction time is 1440 days and the permeation rate in a steady-state condition is 0.24 g/(m d) (Kalbe et al. 2000)...

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